There are several types of sights utilized with small arms, such as rifles, shotguns, hand guns, bows, and other similar, hand-held weapons.
One type of sight known in the art is a holographic sight. In a holographic sight, a laser beam of light is transmitted through a housing and is reflected one or more times until an aiming reticle image is generated by a hologram element. Diffraction gratings can be implemented in these and other types of optical sights. The diffraction grating spatially directs light in the laser beam as the wavelength changes with temperature. The Lightweight Holographic Sight disclosed in U.S. Pat. No. 6,490,060 issued to Tai et al. describes a compact and lightweight design of a holographic sight includes a grating that can also rotate in two axes to adjust light reflected from the grating and shift the aiming reticle.
Some prior gratings are inherently angle- and wavelength-selective, but lack environmental durability. For example, emulsion-based holographic volume phase gratings (VPGs) can be designed and constructed to diffract a single primary order into a very specific direction. Other prior gratings are inherently durable, but lack angular and wavelength selectivity. For example, ruled metal-on-glass gratings and metal-on-epoxy replicated gratings are capable of diffracting over wide ranges of wavelengths, including multiple orders of each input wavelength. Each output angle may include primary and higher diffraction orders unless order-sorting filters are added to the optical path. It is therefore desirable to combine wavelength selectivity and durability within a single grating technology.
Unfiltered ambient light might enter the housing of the optical sight. This unwanted ambient light can sometimes disrupt the view of the reticle image. This is at least partially due to the ambient light diffracting and reflecting back to the user, causing a visible spectrum of light (i.e., a rainbow) or bright mirror reflections. It is thus desirable to provide a weapon sight that reduces negative effects of ambient light (such as glare) without increasing the size of the sight. It is also desirable to improve existing weapons sights to reduce the negative effects of ambient light while considering the cost, weight, and number of parts in the sight.